p0420
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Honda · SUVs
Catalyst System Efficiency Below Threshold Bank 1
Quick Answer
Error code P0420 on your Honda SUVs means: Catalyst System Efficiency Below Threshold Bank 1. This is usually fixable — see the step-by-step guide below.
Affected Models
Applies to all models
RW1RW3RW5RV1CR-V EX 2024CR-V EX-L 2024CR-V Hybrid Sport 2024CR-V Hybrid Sport Touring 2024CR-V Hybrid Sport-L 2024CR-V LX 2024CR-V Sport 2024CR-V Sport Touring 2024HR-V EX-L 2024HR-V LX 2024HR-V Sport 2024Passport EX-L 2024Passport Sport 2024Passport Touring 2024Passport TrailSport 2024Pilot EX 2024Pilot EX-L 2024Pilot Elite 2024Pilot LX 2024Pilot Touring 2024Pilot TrailSport 2024YG7YA7ZD1RZ1
Likely Causes
How to Fix It
1
Resolve any other DTCs first, especially misfire or fuel system codes, that could cause secondary catalyst damage
2
Compare upstream and downstream O2 sensor waveforms with a scan tool; downstream should be nearly flat if the cat is working
3
Inspect for exhaust leaks at the manifold flange, flex pipe, and catalytic converter joints
4
Measure catalytic converter inlet and outlet temperatures with an infrared thermometer; outlet should be hotter during normal operation
5
Replace the catalytic converter with an OEM or CARB-compliant unit if efficiency is confirmed below threshold
Pro Tip
This issue typically requires professional diagnosis. Attempting this fix without proper training could cause further problems.
Parts You May Need
Catalytic converter (OEM or CARB-compliant)
Downstream oxygen sensor
Exhaust gaskets and flange hardware
Exhaust flex pipe (if cracked)
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